Flexible exhaust pipe joint



Sept. 15, 1942. w. L.. LEWIS FLEXIBLE EXHAUST PIPE JOINT Filed oct. 9, 1940 Patented Sept. l5, 1,942

FLEXIBLE axmms'r ma .lolNr william n Lewle, Glendale, can., einer te' Hughesv Tool Company, poration of Delaware Houston, Tex., a oor- Application oetebell s, 1940, serial Ne. Senasa z chillin...l (ci. ass- 11) My invention relates to pipe joints with special reference to exhaust pipes for internal combustion engines, and is directed specifically to a flexible exhaust-pipe joint foraircraft.

Aircraft engines are commonly mounted in a resilient or floating manner to permit engine vibration to be dissipated instead of transmitted All metals and coatings within my knowledge heretofore employed for the relatively movable surfaces of such exible joints have either galled from friction alone or haveV roughened to an indirectly to the main aircraftk structure. A portion of the 'exhaust rectly on the system is, of course, mounted diengine to move with the engine relative to the aircraft structure, but the major portion of the exhaust system may be fixed to the aircraft structure not only because it is usually necessary to carry the exhaust gases a substantial distance rearward from the power plant. but also because exhaust ducts are commonly incorporated in heating combinations and other devices that are rigidly mounted on the aircraft structure. The need arises, then, for a flexible joint to interconnect that portion of an exhaust duct that is carried by the' vibrating engine and the continuing portion of the exhaust duct thatV is rigid relative to the aircraft proper.

To minimize fire hazard and prevent the accumulation of obnoxious and lethal gases in the aircraft, such a joint mustbe substantially gastight, and also act as a lire seal. A gas-tight exible joint effective for such service is not easily attained. The exhaust gas is above atmospheric pressure and pulsates in a forceful manner `that favors leakage; The high temperature of the exhaust not only expands the interconnected elements of the joints, but also tends to break down many sealing elements that might be employed.

Acids and other corrosive high temperature products of combustion present serious problems. Fi-

for such a exible joint.

operative degree because of friction, together with' high temperature in the presence 4of the corrosive constituents of the exhaust. All steel alloys tried, including stainless steel, gall badly in' a short time even if highly polished. Cadmium, zinc, copper and nickel coatings either gall promptly or completely break down from corrosive action and high temperatures.

The general object of my invention is to provide a flexible exhaust-pipe joint that is eiiicient mechanically, gas-tight, and long-lived in service. Underlying my invention is the discovery that, contrary to the expectations of those skilled in the art, chromium may be employed to provide rubbing surfaces of the characteristics required Polished chromium surfaces coact with exceedingly low friction, -withstand high temperatures, and resist over long,V l

periods of time the corrosive constituents of anV particular object of my invention, then, is to provide an eective flexible joint incorporating chromium rubbing surfaces.

The above and other objects of the invention will be apparent in the description to follow, considered with the accompanying drawing.

In the drawing which is to be taken as illustrative only:

Fig. l is a side elevation of a portion of an aircraft showing the invention incorporated in an nally, flexibility in such a joint is usually achieved by employing overlapping friction surfaces where leakage might occur, especially since the surfaces are' in continual relative movement to accommodate the changes in angular and spatiall relationships, between the movable and xed portions of the exhaust duct. 4

With the advent of larger and more powerful aircraft engines, the problem of avoiding intolerable leakage between the relatively movable surfaces of flexible exhaust joints has become exl ceedingly diflicult to` solve. The larger andmore powerful engines have larger amplitudes of vibrationso that the range of angles that must be accommodated by a short-coupled joint is greatly increased. Because of the larger engines, the exhaust pipes must be of relatively large diameter, a fact that further fa ors leakage in a flexible joint.

` by the line 3 3 of Fig. 2;

Fig. 4 is a greatly enlarged fragmentary section `taken as indicated by the line 1 4 of- Fig. 2;

exhaust system; e,

Fig. 2 is a section on an enlarged scale taken as indicated by the line 2--2 of Fig. l, a portion of the view being in side elevation; Fig. 3 is a transverse section taken as indicated Fig. 5 is a fragmentary section on a greatly enlarged scale taken as of Fig. 2; and

Fig. 6 isa section line 6--6 of Fig. 5.

Shown in dash-lot lines in Fig. 1 is a fragmentary portion of an aircraft structure, generally' designated I0, an aircraft engine Il, and a propeller l2 driven by the engine. Part of the aircraft`structure IU is a frameworkincluding arms I3 and a ring I5 for direct support of taken as indicated by Vthe Vthe engine Il, the engine being resiliently andY flexibly mounted on the ring member ls in a indicated by the line 5 5 general configuration of a ring, t'ached to the engine by branches l1 that in- 2 well known manner permitting free. vibratory movement of the engine relative to the ring.

An exhaust manifold I6, which also has the is rigidly atdividually connect with the variousexhaust ports of the engine. A flexible exhaust pipe joint, generally designated 20, constructed as taught herein, carries the exhaust gases from the vibratory manifold I6 to an exhaust tail pipe 2| that is rigidly carried by the aircraft structure |6. The preferred form of the flexible joint 26 will now be described.

The manifold I6 terminates in a short exhaust duct 22, and on the end of the exhaust duct is attached in a gas-tight manner a joint element in the form of a ring 23 having a spherical chromium surface 25. The spherical surface 25 may be either concave or. convex, lbut in the instant construction is convex. The tail pipe 2| which constitutes the fixed portion ofthe exhaust system has on its inlet end a joint element in the form of a ring 26 having a spherical chromium surface 21. This second spherical surface 21 may also be either concave or convex, but is shown as concave in the drawing. The ring 26 may constitute a flared portion of a sheet metal collar 28 that nests into the end of the tail pipe 2| and is welded or otherwise secured to the tail pipe in a gas-tight manner.

'Ihe body of the flexible joint 20 is preferably extensile axially and may consist of two slidingly telescoped cylinders 30 and 3| having over-- lapping portions 32'and 33 respectively. It is contemplated that the overlapping portions 32 and 33 will have chromium rubbing surfaces that fit together sufficiently close to substantially preclude any g'as leakage.

At the outer end of the cylinder 30 is fixed a joint element in the form of a ring 35 having a spherical concave chromium surface 36 complementary to the convex spherical surface of the previously mentioned ring 23. The ring 35 may that is iixedly telescoped into the end of the cylinder 30. To cooperate with the fixed ring 26 cn the inlet end of the tail pipe 2| the second cylinder 3| of the joint 2li has at its outer end a joint element in the form of a ring 36 having a convex spherical chromium surface 40 that is complementary to the previously mentioned spherical surface 21.

The above described construction comprises in essence a cylindrical joint body having ball-andsocket connections with the adjacent portions of the exhaust duct, each pair of the coacting jointelements or `rings constituting in eiecta universal joint. All of the described spherical surfaces are formed on centers of curvature lying on the axis of the exhaust duct so that intimate contact precluding gas leakage may be maintained over the range of angles through which the joint may be disposed by vibratory movement of the engine relative to the aircraft structure/Ill.

Various expedients may be employed to mainv tain the required intimate mutual contact of.

the coacting spherical surfaces 25 and 36 at one end of the joint and of the coacting spherical surfaces 21 and 4l) at the other end of the joint. In the particular construction shown in the drawing, the means for maintaining the required intimate contact comprises yielding means in the form of a series of helical springs 4| that be the flared portion'of a sheet metal collar 31 tend to spread the twocylinders 30 and 3| axially apart.

The springs 4| may be mounted on the joint in any suitable manner. In the particular construction shown, a plurality of brackets, generally designated, in this case three brackets,

are mounted on the periphery of the cylinder 30 and are paired with a second plurality o f similar brackets, generally designated 43, on the periphery of the cylinder 3|. Each of the brackets 42 carries a stud 45 that telescopes into a stud 46 carried by the corresponding-bracket 43, and each of the springs 4| is mounted on one of these coacting pairs of studs in 'compression between the corresponding brackets.

The brackets 42 and 43 may have various constructiona In the particular arrangement the drawing, each bracket 42 or 43- shown in includes a pair of small projecting plates 41 that have overhanging portions 48 spaced apart to form a radial slot 50, the slot being dimensoned to vreceive a reduced end 5| of one of the studs 45 or 46. Each of the small projecting plates 41 is braced by a wing 52, and for further reenforccment a washer 53 is welded across each pair of the plates 41, the washer having a slot 55 registering with the previously mentioned slot 50.

To assemble one of the studs 45 or 45 to one of the brackets 42 or 43, a washer 56 is placed en the reduced end 5| of the stud against an annular shoulder 51 of the stud and then the stud is moved into the slots 5|] and 55. A castellated nut 58 is then threaded onto the reduced end 5| of the studv and anchored by a suitable Cotter pin 59. The washer 56 is cut away to provide straight edges 60 (Fig. 5), complementary to the inner edges of the projecting plates 41, and in its iinal assembled disposition is in the plane ofV the projecting plates 41 to be retained by the overhanging portions 48.

It is vapparent that the three springs 4| in continuously tending to .extend the body of the flexible joint 20 cause the described ball-andsocket members at the ends of the d,joints to maintain effective sealing contact at all the angles to which the joint may be disposed in service. Although suicient pressure is applied to prevent any intolerable gas leakage, the joint moves freely because polished chromium surfaces in mutual contact develop little friction even under relatively high pressure.

While the relatively movable parts of the described joint construction may be made of a suitable chromium alloy with suitably polishedgether. Thus in Fig. 4 I show chromium plating 8| on the periphery of the cylinder 30, chromium plating 62 on the complementary inner surface of the cylinder 3|, chromium plating 63 on the spherical surface 40 of the ring 38, and chromium plating 64 on the complementary spherical surface 21 of the ring 26.

The construction described in specific detail herein for the purpose of illustration will suggest to those skilled in the art various changes and modifications.- The right is reserved to all such departures from the described construction that properly come within the scope of the appended claims.

I claim as my invention:

1. In an internal combustionengine exhaust duct subject to the action of hot corrosive gases,

the combination of: a first hollow ilxed relative to the engine and -forming a portion of mentary to and in' Irictional contact with said ilrst sealing'surface.

2. In an internal combustion engine exhaust duct subject to the action of hot corrosive gases, the combination of: a ilrst hollow body forming a portion-of said duct; -a secondhollow' forming an adjacent portion of said duct said iirst hollow body being telescoped into said second` r hollow body for relative movement to rmitv ex-4 tension and contractionof the duct incidental to engine vibration; and means to prevent the corrosive action of said gases comprising a firstcylindrical chromiumsealing surfaceon the outside 'of said rst hollow body concentric to a center in vsaid duct, and; a second' cylindrical chromium sealing surface on the' inside of an adjacent portion oi said second hollow body concentric to said center, said second sealing surface being complementary to and in frictional contact with said rst sealing surface. v v

WILLIAM L. LEWIS. I 

